The invention relates to storage devices in general, and in particular to a storage device having a superset format, and a method and system for using the storage device. Manufacturers find it desirable to use common parts across multiple products. Common parts reduce part cost since it is possible to order and purchase larger quantities from suppliers. Higher volume purchases translate into less per unit costs. Order volume of common parts will increase as the part is used in more and more server models and machine types. Take for example 5 individual power supply designs that have orders for 1,000 parts each. If the 5 individual power supply designs could have been a single common design, there would now be a single order for 5,000 of the common power supply in all likelihood at a reduced per unit price. More common parts reduce inventory costs and manufacturing carrying charges by making the manufacturer less dependent on the accuracy of machine-type and model sale forecast projections.
Fewer, more common parts, should result in fewer quality problems. Significant reductions in the number of unique parts should provide the opportunity to do a better, more thorough job of bringing parts into the business and managing them with the same resource. Qualification and testing would also be more thorough. This is especially important where subtle differences in operating characteristics of complex electronics can result in intermittent difficult-to-diagnose problems. Fewer more common parts provide more opportunity to second source parts that can be leveraged if quality problems with a particular supply line arise.
Computer systems often require a considerable amount of nonvolatile disk storage to preserve software, programs and other data that can not fit in the smaller more costly RAM memory and that otherwise would be lost when the system is power is turned off. At present, it is common for these storage systems to be built using a large number of Hard Disk Drives (HDDs). HDDs are constructed using one or more disk shaped platters coated with a magnetic material. The disk platters spin at fixed speeds and a movable arm with a read/write head is directed to specific locations on the disk to write data or read data. The head assembly glides just above the surface of the platter. During a data write operation it applies an electric field to a specific location on the disk creating a substantially permanent magnetic field in a specific direction. If the field points in one direction it represents a binary “1” and if it points in the other direction is represents a binary “0”. The head assembly is designed to read stored data by sensing the small current induced in the head assembly by the magnetic field when in passes over the magnetized location on the platter. When the HDD is powered off, the data is preserved by the magnetic signature, the bits of information at specific locations on the disk.
HDD platters are partitioned into concentric circles called tracks that are coincident with areas over which the head glides when the arm assembly remains motionless. Each track is further partitioned into sectors. Each sector contains a larger fixed length area for the customer data as well as header and trailer information used by the HDD electronics during the data storing and retrieval process. Data read and write times called latency are not fixed and predictable as they are in RAM. The latency, to a large extent, is a function of the seek time, the time it takes the arm to reposition the head over the track where the data is to be stored or retrieved. That time is variable and a function of the last position of the arm.
Each HDD platter is formatted, pre-written, with data used by the electronics and microcode in the HDD and HDD adapter to store and retrieve data. The formatting typically involves sector header and trailer information as well as a standard fixed size data field where a set number of bytes per sector are allocated to store user data. It is common for HDDs to contain not only user data but a small area of “nonuser” data where vital product data (VPD), information useful to the operating system or firmware, is stored. For example, IBM eServer® systems have evolved with unique formats fine tuned to enhance system performance. For example, xSeries and pSeries utilize 512 bytes per sector formats. However there are some subtle format differences in VPD between pSeries and xSeries that prevent plug compatible substitution. iSeries uses 522 bytes per sector that is an artifact of the OS/400 operating system as well as providing enhanced data integrity capability. Total Storage systems typically have 524 bytes per sector. FIG. 1 depicts three exemplary hard formatted sectors. The first sector features 512 bytes per sector, the second sector features 522 bytes per sector and the third sector 524 bytes per sector. The bytes per sector are fixed and a sector cannot accommodate a different format. There are also different HDD functional requirements (e.g. skip read/write, error recovery) between the eServer systems which result unique HDD firmware per Series.
HDDs are typically designed as self contained assemblies that can be plugged into a standard slot in the computer chassis or in a separate storage chassis. Separate storage drawers typically hold anywhere from a half dozen to as many as 50 or more individual HDDs. A storage chassis can be either a stand-alone assembly or a rack mountable unit to allow multiple drawers to be placed into a single rack creating a relatively large array of HDDs in a small physical foot print. Drive density per unit area floor space is a competitive metric used in the industry to help potential customers compare offerings from different vendors.
The storage capacity of computer systems often needs to be increased. Currently, adding storage capacity involves purchasing additional HDDs and either scheduling time for a customer engineer to bring the new equipment and install the HDDs in the system or waiting for HDDs to be shipped directly to the customer location and installed by the customer. In addition, if the customer's storage drawers are already filled to capacity, new storage drawers would need to be purchased and installed. Additional racks might also be required.
Different computer systems often require HDDs with different formats which need to be stocked and inventoried as distinct parts with unique part numbers. The greater the number of unique parts, the more complex it is to manage and thus the greater the overall end-to-end costs a business will incur.
HDD technologies continue to evolve. Higher density, greater speed devices, different types of disk device are being created at an ever accelerating rate of change creating an extraordinarily large number of device types and part numbers that need to be supported driving up inventory, scrap, quantity of field spares and other end-to-end costs. It is desirable, in order to simplify manufacturing operations, field service support, and customer operations to reduce the number of unique HDD PNs.